Thorium-beryllium alloys and method of producing same



Sept. 8, 1959 F- H- SPEDDNG ETA'- 2,903,351

'I'HORIUM-BERYLLIUM ALLOYS AND METHOD OF PRODUCING SAME Filed April 1l.1949 gl l I n u l g nl f a 5 4 a' ,amy

United States Patent O THORIUM-BERYLLIUM ALLGYS AND METHOD F PRODUCINGSAME Frank H. Spedding and Harley A. Wilhelm, Ames, Iowa, and Wayne H.Keller, St. Louis, Mo., assignors to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationApril 11, 1949, seria1No.s6,'/3s

9 Claims. (el. 7s1zz.7)

This application relates to the production of alloys from halides of therefractory metals, by which We intend to encompass all metals whosemelting points are higher than 1600 C., and to the alloys producedthereby. The invention especially deals with alloys containing thorium,titanium, zirconium, and hafnium, the metals of group IVB of theperiodic system.

This application is a continuation-impart of our copending application,Serial No. 695,299, tiled September 6, 1946, now U.S. Patent No.2,782,116, granted on February 19, 1957.

The production of thorium has been proposed by reaction of the oxide,chloride or other compound of the desired metal with sodium metal.However, it has been found that such processes result in the productionof the metal in a linely divided or pulverulent state, frequently in lowyield, and in most cases the metal produced, whether in massive form orpowdered state, has been contaminated with numerous impurities,particularly with the oxide of the metal undergoing preparation. Suchmpurities are very disadvantageous for the production of alloys becausethe mechanical properties of the nal product are greatly impairedthereby.

The present invention provides a novel process whereby the metals hereincontemplated may be produced and alloyed in situ and obtained in massiveform (as relatively large aggregates) substantially free fromimpurities, particularly the oxide of the metal to be produced. Inperformance of the process, a reducing metal of the group consisting ofalkali metals and alkaline earth metals such as sodium, potassium,lithium, calcium, barium, strontium or magnesium (usually in an excessof to l0 percent or more of the theoretical quantity required), isreacted with a iluoride of the refractory metal to be alloyed. Variousmetals which are below the refractory metal in the electromotive seriesmay be simultaneously reduced by this process, together with therefractory metal, from their halides, whereby corresponding alloys areobtained. The halides of the metals of groups IIA, IIB, IIIA, IVA, andVA are suitable for co-reduction with the abovenamed refractory metalsof group IVB of the periodic system.

We have found that such a process should be conducted at a temperatureabove the melting point of the metals being prepared or at least at atemperature suiciently high to form a molten metal phase and to maintainthe resulting reaction mass in molten state for a time sutlicient topermit separation of a molten pool of metal from the resulting slag,which comprises the uoride of the reducing metal. This pool of moltenmetal may be withdrawn While the metals remain in molten state, or thepool may be allowed to solidify and be separated from the slagthereafter. Calcium and magnesium and similar alkaline earth metals areespecially useful as reducing metals in this process.

The development of sufficient heat in the reaction mixture to establishthe reaction temperature and to maintain the reaction mass in moltenstate until separation of the phase into layers has been secured, isimportant since, if the temperature is not high enough, the reactionwill be incomplete and recovery of metal poor. With certain fluorides ofmetals which melt at lower temperatures and certain reducing metals,such as calcium, suthcient heat may be developed by the exothermicreaction to effect this desired result, provided proper precautions aretaken to prevent loss of heat through the walls of the reactor and alsoprovided that suicient reaction mixture is used in the reactor. On theother hand, special precautions must be resorted to in order toestablish and maintain the required temperature for production of therefractory-type metals and alloys herein desired to be produced sincethey melt at temperatures up to l600 to l800 C.

In accordance with this invention, it has been found that all, or asubstantial portion of, the necessary heat required to ensure layerseparation is developed internally by the simultaneous reactioninvolving co-reduction of said above-mentioned other metal halides inthe reaction mixture of the refractory metal fluoride and the reducingmetal. 'This second reaction is thermodynamically capable of developinga temperature higher than can be developed by the reaction of thereducing metal with the rcfractory metal fluoride alone. For example, anadditional halide of another metal which, in the electromotive series,is below the reducing metal and below the refractory metal beingproduced, may be added to the reaction mixture, and the amount ofreducing metal (calcium, magnesium, sodium, etc.) is increasedaccordingly. By this process, heat evolved from the second reaction aidsin the establishment of the temperature required, and/ or the presenceof said second reactants or reaction products lowers the melting pointof the metals and/ or slag so that the layer separation may be secured.A particularly advantageous result may be obtained by the reduction of amixture of the refractory metal liuoride and a chloride of the othermetal, since in such a case the reaction heat is noticeably increasedand, in addition, the fluidity of the resulting chloride-uoride slagand/or the melting point thereof is sufficiently low to permit veryefficient separation of the alloy formed therefrom so that the resultingalloy is secured in high yield and good purity.

Alloys of thorium-beryllium, thorium-aluminum, thorium-zinc,thorium-bismuth, for instance, may be produced in this manner. Therelative proportions of refractory metals to other metal may be adjustedwithin comparatively wide limits in accordance with results desired.Where the metal which is coproduced with the refractory metal isextremely light as in the case of beryllium, the quantity used of saidother metal halide should be balanced if possible so as to avoidproduction of a metallic mixture having approximately the same densityas the slag.

In conducting the reaction, we have found that it is desirable toestablish a superatmospheric pressure upon the reaction mixture whilethe reaction is proceeding in order to maintain the reducing metal moreor less uniformly dispersed throughout the reaction mass and thereby toensure production of the resulting alloy in comparatively high yield.Where an alloy of high purity is desired, the pressure may be releasedafter substantial reaction has occurred and many of the impurities canthen be distilled from the molten metal. Alternatively, the moltenmetals may be allowed to solidify and subseifquently may be remelted andimpurities distilled thererom.

Particularly advantageous results may be secured if the reaction isconducted n an elongated reactor of each height that the resultingmolten pool of metal will have a minimum surface area in order tominimize loss of heat and premature solidification of the metal.

The reactor is usually constructed of iron or steel. The problem ofsecuring a satisfactory lining is of paramount importance. The metalsundergoing reduction as herein contemplated in general alloy readilywith iron or steel. Should the lining become defective during theoperation, metallic thorium or similar metal tends to flow through thedefect to the metal wall of the reactor and to penetrate the wall, thuscreating an exceedingly hazardous condition due to the fact that themolten metal flowing through the opening created in the wall reactsviolently with the air.

The problem of securing suitable linings for bombs or other reactorsused in this process has been rather complex. Silicates have been foundto be unsuitable because the reducing metals tend to react therewith andto contaminate the metal produced. Applicants have found it especiallyadvantageous to use a reactor which is provided with a lining orinterior surface comprising a refractory compound, preferably lan oxide,of a metal above the metal undergoing reduction in the electromotiveseries which is preferably less volatile than the metal being produced.Alkaline earth metal oxides are particularly valuable for this purpose.

The lining may be deposited upon the walls of the reactor by anyconvenient means. In accordance with one process described in aco-pending application of Harley A. Wilhelm, Serial No. 567,284, filedDecember 8, 1944, now U.S. Patent No. 2,785,064, granted on March 12,1957, an elongated cylindrical bomb provided with a centrally disposedmandrel of the size required for the reaction zone is filled with finelypowdered anhydrous magnesium oxide, dolomitic oxide, calcium oxide orsimilar oxide, 'and the bomb is subjected to a rapid jolting actionwhereby the powder becomes compacted into an inherent well-bondedlining. Thereupon the mandrel is removed and the bomb is ready for use.Details on the construction of the reactor suitable for the process ofour invention are fully described and illustrated in said application ofHarley A. Wilhelm, Serial No. 567,284.

As previously noted, the process may be effectively conducted in anelongated reactor having a length at least three times its width ordiameter, since the use of such a reactor permits ready establishment ofa slagged metal pool of minimum surface area. A cylindrical pipe orshell provided with closed top and bottom ends is suitable. These closedends may be sealed if desired. In general, where a highly volatilereducing metal, such as magnesium or sodium, is used, it is foundpreferable to mount the top or covering end upon the cylinder in amanner such that a minor amount of leakage of gas can take place so thatthe pressure in the reactor during the reaction does not becomeexcessive, being in such a case, below the autogenous pressure of thesystem and rarely above a few hundred lbs./sq. in. and frequently belowabout 100 lbs./ sq. in. The amount of leakage permitted, however, shouldnot be so great as to prevent establishment of a superatmosphericpressure within the reactor by the reactants. A tlange cover fitted tothe top end of the reactor without a gasket provides a sufficientlyloose fit.

The reactants should be anhydrous and substantially free from oxygen.The reactants should be thoroughly mixed prior to introduction, and, inorder to secure satisfactory mixing, the reducing metal should be nelydivided (generally `about -10 to -50 mesh). In most cases the fluorideundergoing reduction may be much iiner, its particle size usually being-100 mesh. Sufticient reaction mixture is used substantially to till thereactor.

Following charge of the reaction mixture into the lined reactor, a coverof the lining material s provided, and the reactor is closed. Thereaction is initiated by preheating until the reaction mixture or aportion of it or one or more of the components thereof has been heatedto the temperature at. which reaction will take place 4 (about 400 to600 C. or higher), or, where preheating is unnecessary, the reaction maybe initiated by means of an electrical fuse. This fuse may comprise ashort length of resistance wire attached to a suitable source ofelectrical power and functions by heating a localized portion of themixture to the temperature at which reaction initiates (usually about400 to 600 C.).

After reaction has been initiated, substantial pressure develops withinthe system due to vaporization of the reducing metal or halide and dueto the fact that escape of the metal or vaporized halide is prevented orsubstantially minimized. 'I'he pressure developed in general exceeds 0.5to 3 atmospheres gauge and in some cases is of the order of 75 to 100lbs/sq. in. gauge or higher it serves to maintain the reducing metalmore or less uniformly dispersed throughout the reaction mixture asreaction proceeds. This facilitates substantially complete reaction ofthe halide salts and also tends to prevent reversal of the reaction atthe elevated temperature due to back reaction of the resulting metalwith the slag or the calcium oxide or other oxide of the liner.Moreover, the pressure prevents or minimizes inleakage of air ormoisture into the reactor.

When a bomb or reactor of elongated construction as herein described isused, particularly advantageous results accrue due to the fact that thereaction may be initiated in one end of the bomb by heating or otherwiseand that thereby a temperature dierential may be established in whichone end is above the boiling point of the reducing metal and the otherend of the reactor is below the boiling point of the metal phaseproduced and frequently at a temperature several hundred degrees belowthat of the opposed end. This is found to be advantageous, since iteffectively minimizes establishment of excessive pressures in thereactor. Furthermore, after reaction is over or begins to subside andcooling of the reactor begins to occur, distillation of the reducingmetal from the molten mass takes place, and this metal condenses in thecooler end of the bomb. Thus, the temperature differential establishedpermits substantial puriiication of the metal by removal of reducingmetal, halides and other impurities as the metal is being cooled to thesolid state.

After the reaction is completed, the molten mass is maintained in themolten state until the alloy has substantially completely separated fromthe slag. Usually this requires one or several minutes. Thereafter thealloy may be allowed to solidify into a solid ingot, or it may bewithdrawn from the reactor in the molten state.

The resulting alloy is comparatively free from impurities although itmay contain small amounts, for example one or several percent, ofmagnesium, calcium, or other reducing metal which has been used toeffect the reaction, and it also may be contaminated with the addedmetalhalide or its reaction product. For example, when thorium iluoride andzinc chloride are coreduced, the resulting product will be a mixture ofalloy of thorium and zinc, and similar results are secured when halidesof metals other than zinc are used in conjunction in the process hereincontemplated. Further impurities may be present due to the use ofreactants which are impure, and, in addition, some thorium or otherrefractory metal oxide may be present due to partial reaction of therefractory metal with the lining and/or due to the presence of aresidual amount of water n the mixture or reactor lining.

As previously stated, a substantial purification of the alloy may besecured by heating it in vacuo at a temperature at which it is molten.In order to secure a satisfactory purification and prevent furtheroxidation or contamination of the metal, this treatment is preferablyconducted in a closed crucible or melting chamber constructed ofgraphite or similar inert material, and the absolute pressureestablished within the crucible is generally below about 1 to 2 mm. ofmercury and frequently of the order of 100 to 200 microns. Impuritiessuch as magnesium, calcium, or other alkaline earth metal, sodium,potassium or other alkali metal, boron, silicon, cadmium, or othermetals, phosphorus, sulfur, and halogens are removed to a verysubstantial degree by this process. The temperature of melting usuallyis 100 or 200 above the melting point of the alloy undergoingpurification treatment but below the boiling point of such metal.

After impurities have been distilled from the molten mass, the moltenmetal may be drained from the crucible and cast into suitable ingots. Afurther puriiication of this metal is thus secured, since thenon-volatile impurities, including oxides, tend to form a scum or film,particularly where the temperature of melting is maintained below themelting point of the respective oxides of the metals undergoingtreatment. In such a case the oxides remain essentially solid orsemi-solid, and the metal flows from' the oxide which in turn tends toadhere to the walls of the crucible or at least to separatesubstantially from the metal.

The following examples are illustrative.

Example I duced:

Lbs. Thorium uoride 17.05 Zinc chloride 3.77 Calcium 6.65

The charge was weighed and mixed in a dry room, precautions being takento prevent absorption of an appreciable amount of moisture by the zincchloride. A layer of dry calcium oxide was packed on top of the chargeand the top flange was bolted on. The bomb was inserted in a gas burnerfurnace, leaving the end which had the ilanged cover exposed to theatmosphere. The temperature of the furnace was 1160 F. and the reactioninitiated in fourteen and one-half minutes. The top of the reactor wasat a temperature several hundred degrees below that of the centralportion. Several minutes after the reaction initiated, the bomb wasremoved from the furnace and cooled with a water spray. The top flangewas removed, and an ingot weighing about 13 lbs. and having thefollowing analysis was obtained:

The process described in Example I was repeated using a sintered calciumoxide crucible in an iron bomb 2.5" by 12" and using the followingcharge:

G. Thorium uoride 250 Beryllium uoride Iodine 205 Calcium 121 The bombwas heated to 656 C. and the reaction initiated at this temperature.After cooling, a thoriumberyllium alloy which was quite malleable andquite resistant to corrosion was secured in the form of a massive ingot.k

Example III The process of Example 1I was repeated using the followingcharge:

A thorium-beryllium alloy was secured containing about 17% by weightberyllium and 83% by weight thorium. The product produced was hard andquite resistant to corrosion.

By the process of the invention, thorium-beryllium alloys may beprepared which have the two components in any ratio possible. As littleas 0.5% beryllium, or even less, causes a reduction of the melting pointof thorium by as much as 500 C. These alloys having a low berylliumcontent are easy to cast, and they are considerably more resistant tocorrosion than pure thorium.

The -attached drawing contains curves in which the corrosion resistanceto air at various temperatures of a 2% beryllium-thorium alloy iscompared, by way of example, with that of pure thorium. It will bereadily seen how favorable an effect the addition of 2% beryllium has onthe corrosion resistance.

Another interesting alloy of the numerous ones produced by the processof our invention is that containingA 94% by weight of beryllium and 6%by weight of thorium. This alloy crystallizes in the cubic system. Ithas a highly increased degree of malleability as compared with that ofpure bryllium.

Example IV The process of Example III was lrepeated using a mixture ofbismuth and thorium uoride in the proportion of 1 mole Th1-l,b to 1/3mole BiF3 to 3 moles calcium metal. Thorium-bismuth alloy separated andwas recovered.

The invention is particularly concerned with, and has been describedwith particular reference to, the production of thorium Ialloys.However, the principles herein disclosed may be applied to theproduction of other alloys of the refractory metals. For example,liuorides of other high-melting metals such as hafnium, chromium,titanium, zirconium, tungsten, tantalum, or similar metals of the groupIVB, group VB and group VIB, which melt at 1600 to 1800 C. or above, maybe reduced with zinc chloride, cadmium chloride, or similar chloride orother halide of a B group metal as above-listed.

The invention as herein described has been particularly concerned withthe production of the metals from their uorides which have the generalformula MFz where M is the metal concerned and x is a small wholenumber, usually being 2, 3, or 4, depending upon the respective valenceof the metal. However, where the liuoride is highly volatile, as in thecase of TiF4, it is desirable to avoid use of such a uoride because ofthe high pressures developed. In such a case more complex, less volatilefluorides, such as NazTiFG or KzTiF or the correspond ing zirconiumcompounds may be used. The process may be used in connection with theproduction of metals from other halides such as chlorides, bromides, oriodides of the above metals. At the same time, however, production ofmetal from these compounds may be disadvantageous in some cases due tothe high pressures which may be developed in the reactor and also due tothe hygroscopicity of the chlorides and similar halides. Thehygroscopicity of some of these halides is particularly objectionable,because the water thus introduced reduces the yield of metal and makesthe separation of the molten phases more diicult. In consequence, it ispreferred to conduct the reactions herein contemplated using thefluoride. However, mixtures of uoride and chloride may be used aspreviously described, and in such a case increased fluidity in the slagpermits a more complete recovery of the metals produced. Similar resultsmay be secured by using other chloride-fluoride mixtures, or othermixtures of metal fluorides with metal halides. For example, a mixtureof ThF4 and ThCl4, ThBr4, or ThI4 may be co-reduced. Likewise, a mixtureof ThCl4 and ZnF2 may be reduced as herein contemplated. Moreover,halides of chromium, zirconium, etc., such as chromic chloride, chromicuoride, or other of the refractory metal halides may be reduced by thisprocess. Where the simple halides are undesirable because of their highvolatility, less volatile halides, such as NazTiF, K2TiF6, or Na2ZrP6may be reduced by the present process.

While the invention is particularly concerned with the reduction ofhalides of refractory metals above-dened, it may be advantageouslyapplied to reduction of metal halides generally. Thus, the co-reduction,by means of a metal higher in the electromotive series, of a fluoride ofa metal lower in the series with another halide of the same or diierentmetal, such yas the chloride thereof, is advantageous to form a moreluid and/ or lower-melting slag which separates more readily from themolten metal formed. For example, beryllium iluoride may be co-reducedwith lead chloride, zinc chloride or cadmium chloride by calcium orsimilar metal as herein contemplated.

Although the present invention has been described with particularreference to the specific details of certain embodiments thereof, it isnot intended thereby that such details shall be regarded as limitationsupon the scope of the invention except insofar as included in theaccompanying claims.

What is claimed is:

1. A binary thorium-beryllium alloy in which thorium is the predominantingredient.

2. A binary-beryllium alloy in which beryllium is the predominantingredient.

3. An alloy consisting of 83% by Weight of thorium and 17% by weight ofberyllium.

4. A binary thorium-beryllium alloy containing approximately 0.5%beryllium.

5. A binary thorium-beryllium alloy containing approximately 2%beryllium.

6. An alloy consisting substantially of 94% beryllium and 6% thorium.

7. A method of preparing a thorium-beryllium alloy, comprising the stepsof simultaneously reducing uoride of thorium and a halide of berylliumwith a metal selected from the group consisting of alkali metals andalkaline earth metals at a temperature sufficiently high to form amolten alloy of said metals, and of maintaining said elevatedtemperature until separation of the alloy from a slag formed has takenplace.

8. A method of preparing a thorium-beryllium alloy, comprising the stepsof simultaneously reducing thorium uoride and beryllium fluoride withcalcium at approximately 650 C., and of maintaining said temperatureuntil the thorium-beryllium alloy has separated from a slag formed.

9. A binary thorium-beryllium alloy.

References Cited in the file of this patent UNITED STATES PATENTS1,648,954 Marden Nov. 15, 1927 1,728,940 Marden Sept. 24, 1929 1,728,942Marden Sept. 24, 1929 1,814,721 Marden July 14, 1931 2,025,614 Rohn Dec.24, 1935 2,193,363 Adamoli Mar. 12, 1940 OTHER REFERENCES Hessenbruch:Nickel Alloys for Use as Pins in Artiiicial Teeth, Chemical Abstracts,vol. 35, p. 6922 (1941).

Baenziger et al.: U.S. Atomic Energy Commission Document No. ABCD-2506,The MBela Compounds; declassied Mar. 2, 1949, 4 pages.

7. A METHOD OF PREPARING A THORIUM-BERYLLIUM ALLOY COMPRISING THE STEPSOF SIMULTANEOUSLY REDUCING FLUORIDE OF THORIUM AND A HALIDE OF BERYLLIUMWITH A METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS ANDALKALINE EARTH AT A TEMPERATURE SUFFICIENTLY HIGH TO FORM A MOLTEN ALLOYOF SAID METALS, AND OF MAINTAINING SAID ELEVATED TEMPERATURE UNTILSEPARATION OF THE
 9. A BINARY THORIUM-BERYLLIUM ALLOY.